Parametric and working fluid analysis of a combined organic Rankine-vapor compression refrigeration system activated by low-grade thermal energy

Journal of Advanced Research (2016) 7, 651–660

Cairo University

Journal of Advanced Research

ORIGINAL ARTICLE

Parametric and working fluid analysis of a
combined organic Rankine-vapor compression
refrigeration system activated by low-grade thermal
energy
B. Saleh
Mechanical Engineering Department, College of Engineering, Taif University, Taif, Saudi Arabia
On-leave from Mechanical Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypt

G R A P H I C A L A B S T R A C T

The effect of boiler temperature on the COPS for different candidates in the basic ORC-VCR system.

E-mail address:
Peer review under responsibility of Cairo University.

Production and hosting by Elsevier
/>2090-1232 Ó 2016 Production and hosting by Elsevier B.V. on behalf of Cairo University.
This is an open access article under the CC BY-NC-ND license ( />

652

B. Saleh

Nomenclature
Latin letters
ALT
atmospheric lifetime, years
CFCs
chlorofluorocarbons
COP
coefficient of performance
CMR
compressor compression ratio
EPR
expander expansion ratio
GWP
global warming potential
h
enthalpy, kJ/kg
HCFCs hydrochlorofluorocarbons
HCs
hydrocarbons
HFCs Hydrofluorocarbons
HFOs hydrofluoroolefins
LFL
lower flammability limit, % by volume in air
M
molecular mass, kg/kmol
m_
mass flow rate, kg/s
NBP
normal boiling point, °C
ODP

ozone depletion potential
ORC
organic Rankine cycle
P
pressure, kPa
T
temperature, °C

A R T I C L E

I N F O

Article history:
Received 7 May 2016
Received in revised form 17 June 2016
Accepted 21 June 2016
Available online 30 June 2016
Keywords:
Working fluids
Organic Rankine cycle
Compression refrigeration cycle
Combined cycle
Low-grade thermal energy

v
VCR
Q_
_
W

specific volume, (m3/kg)
vapor compression refrigeration
rate of heat transfer, kW
power, kW

Greek letter
g
efficiency
Subscripts
b
boiler
c
compressor
e
evaporator
exp
expander
net
net
s
system
sat
saturated pressure
total
total
P
pump
x
quality
1, 2, 3 . . . respective state points in the system

A B S T R A C T
The potential use of many common hydrofluorocarbons and hydrocarbons as well as new
hydrofluoroolefins, i.e. R1234yf and R1234ze(E) working fluids for a combined organic Rankine cycle and vapor compression refrigeration (ORC-VCR) system activated by low-grade thermal energy is evaluated. The basic ORC operates between 80 and 40 °C typical for low-grade
thermal energy power plants while the basic VCR cycle operates between 5 and 40 °C. The system performance is characterized by the overall system coefficient of performance (COPS) and
the total mass flow rate of the working fluid for each kW cooling capacity (m_ total ). The effects of
different working parameters such as the evaporator, condenser, and boiler temperatures on the
system performance are examined. The results illustrate that the maximum COPS values are
attained using the highest boiling candidates with overhanging T-s diagram, i.e. R245fa and
R600, while R600 has the lowest m_ total under the considered operating conditions. Among the
proposed candidates, R600 is the best candidate for the ORC-VCR system from the perspectives of environmental issues and system performance. Nevertheless, its flammability should
attract enough attention. The maximum COPS using R600 is found to reach up to 0.718 at a
condenser temperature of 30 °C and the basic values for the remaining parameters.
Ó 2016 Production and hosting by Elsevier B.V. on behalf of Cairo University. This is an open
access article under the CC BY-NC-ND license ( />4.0/).

Introduction
Nowadays, there are numerous attempts in the utilization of
renewable energies such as geothermal heat, wind energy,
and solar energy as clean energy sources for electricity production or cooling processes. Also, waste heat can be considered
as renewable and clean energy, since it is free energy and there
is no direct carbon emission. Waste heat can be rejected at a

wide range of temperatures depending on the industrial
processes [1].
An ejector refrigeration system and an absorption refrigeration system can be activated by thermal energy source with a
temperature range from 100 to 200 °C. They have several
advantages such as simple structure, reliability, low investment
cost, slight maintenance, long lifetime, and low running cost
[2,3]. Nevertheless, they are not appropriate for thermal

Parametric analysis of a combined organic Rankine-vapor refrigeration system
sources less than 90 °C and are also not appropriate for working in high-temperature surroundings. Furthermore, the minimum cooling temperature could be achieved by both systems is
5 °C [4].
In the present study, an alternative refrigeration cycle using
an organic Rankine cycle (ORC), activated by renewable
energy, combined with a vapor compression refrigeration
(VCR) cycle is suggested for electricity or cooling production.
The ORC is a favorable cycle to convert low-grade thermal
energy to useful work, which can be used to drive the VCR
cycle. Both expander and compressor shafts are directly connected together to minimize energy conversion losses. The
combined cycle has numerous advantages such as the flexibility
to produce power when cooling is unwanted, which makes the
system can continuously use the thermal energy throughout
the year. In summer, all the thermal energy can be converted
to cooling, while only part of the thermal energy is converted
to cooling in spring and fall. No heat is converted to cooling in
winter. When cooling is not needed, all the thermal energy can
be converted to electricity and sent to the grid [5–7].
The working fluid selection has a large influence on the performance of combined organic Rankine cycle-vapor compression refrigeration (ORC-VCR) system. Several studies have
been done on the working fluid selection, i.e. R12, R22,
R113, and R114 for the ORC-VCR system and identified the
most suitable one, which may yield highest coefficient of performance (COP) [8–13]. The refrigerants R123, R134a, and
R245ca were evaluated to find the best one for the ORCVCR system by Aphornratana and Sriveerakul [14]. The
results indicated that R123 achieves the best system performance. An ORC-VCR system activated by a lowtemperature source utilizes R134a was analyzed by Kim and
Perez-Blanco [4]. The minimum cooling temperature could
be achieved by the system was À10 °C. An ORC-VCR system
utilizing two different candidates for the power and refrigeration cycles, i.e. R245fa and R134a, respectively was investigated by Wang et al. [1]. The system coefficient of
performance (COPS) attained approximately 0.5. Six candidates, namely R134a, R123, R245fa, R290, R600a, and

R600, were investigated to determine appropriate working
fluid for ORC-VCR system by Bu et al. [15]. They concluded
that R600a is the most suitable candidate. A combined ORC
with a vehicle air conditioning system using R245fa, R134a,
pentane, and cyclopentane as working fluids was studied by
Yue et al. [16]. Their results indicated that R134a gives the
maximum economic and thermal performance. An ORCVCR system powered by low-grade thermal energy using two
different substances for the power and refrigeration cycles
was studied by Mole´s et al. [17]. They concluded that the best
candidates for the power and refrigeration cycles are
R1336mzz(Z) and R1234ze(E), respectively.
From the aforementioned introduction, it is clear that there
is still a need for screening of alternative candidates for ORCVCR system. The present study concentrates on the production of electricity or cooling from low-temperature renewable
energies such as waste heat or geothermal heat having a temperature around 100 °C. The potential use of R290, R1270,
RC318, R236fa, R600a, R236ea, R600, R245fa, R1234yf,
and R1234ze(E) as working fluids in the ORC-VCR system
is assessed. The performance of the system is characterized
by the COPS and the total mass flow rate of the working fluid
for each kW cooling capacity (m_ total ). The working fluid

653
Compressor

1
Expander
Qb

6

2

Boiler

5

Qe

Evaporator
7

4

Expansion
valve

Qc

Pump
Condenser
3
Fig. 1

3

3

ORC-VCR system schematic diagram.

accomplishes the highest COPS and the lowest m_ total is recommended. The effects of various working conditions such as the
boiler, condenser, and evaporator temperatures in addition to

the compressor and expander isentropic efficiencies on the
ORC-VCR system performance are also investigated.
Configurations of the ORC-VCR system and working fluid
selection
Fig. 1 shows a schematic diagram of the ORC–VCR system.
The system composed of the ORC and the VCR cycle. The features of this system are as follows: (1) the two cycles utilize the
same working fluid; (2) both expander and compressor shafts
are straightway coupled; (3) both cycles use one mutual condenser and (4) the expander power is merely sufficient to power
the compressor and pump.
A substantial characteristic for sorting the ORC-VCR systems is the shape of the temperature against entropy (T-s) diagram. It may be either a bell-shaped as illustrated in Fig. 2a or
it may be overhanging as displayed in Fig. 2b. Another characteristic for sorting the ORC-VCR systems is the pressure
at which the working fluid receives heat in ORC from the
source of heat. At subcritical pressures, the fluid is subject to
a liquid–vapor phase change process during the heat addition
whereas at supercritical pressures such a phase change does
not take place.
The different system processes can be described as follows.
For the ORC: Process (1-2s) is an isentropic expansion across
the expander, Process (1-2a) is an actual expansion across the
expander, Process (2a-3) is a heat rejection process in the condenser, Process (3-4s) is an isentropic pumping process, Process
(3-4a) is an actual pumping process, and Process (4a-1) is a heat
addition in the boiler. For the VCR cycle: Process (3-7) is an
expansion across the expansion valve, Process (7-5) is a heat
addition in the evaporator, Process (5-6s) is an isentropic compression across the compressor, Process (5-6a) is an actual
compression across the compressor, and Process (6a-3) is a
heat rejection process in the condenser. The working fluid leaving the evaporator and boiler is maintained as saturated vapor.
The working fluid selection is essential in the ORC-VCR
systems. A suitable working fluid accomplishes both high system performance and minimal environmental issues. The following concerns should be taken into account during the
working fluids selection: (1) environmental issues: global

654

B. Saleh

(a) T

(b) T

Tb

1

4a

Tb

4s
6s

4s

6a

3

2a

3

Tc

1

4a

2a

2s

Tc

6s

2s
6a

Te

Te

5

7

7

5

s

Fig. 2

(a) Bell-shaped T-s and (b) overhanging T-s diagram of the basic ORC-VCR system.

warming potential (GWP), atmospheric lifetime (ALT), and
ozone depletion potential (ODP); (2) safety aspects: flammability, toxicity, and auto ignition and (3) economics and
availability.
Hydrofluorocarbons (HFCs) have been selected as working
fluids replacing chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in ORC, VCR cycle, and combined
cycles due to their zero ODP. Because of the HFCs have a high
GWP, they are now being controlled. Accordingly there is still
a continuous search for alternative working fluids, which
might have a better cycle performance, lower atmospheric lifetimes, and lower manufacturing costs, or are preferable due to
toxicity or flammability reasons. One possibility is using
hydrocarbons (HCs), which have a very low GWP and excellent thermophysical properties [18]. The HCs are chemically
stable, non-toxic, highly soluble in mineral oils and environmentally friendly, but they are flammable. Presently, the main
HCs considered as working fluids are R1270, R290, R600a,
and R600 [19,20]. Also, many hydrofluoroolefins (HFOs) with
low GWP are suggested as working fluids [17,21].
In this study, 10 HFCs, HCs, and HFOs, i.e. R1270, R290,
RC318, R236fa, R600a, R236ea, R600, R245fa, R1234yf, and
R1234ze(E) are proposed as candidates for the ORC-VCR system. The basic thermodynamic properties, and safety and envi-

Table 1

s

ronmental aspects of the candidates are listed in Table 1
[22,23].
Mathematical model and computational procedure

The thermodynamic mathematical model for the ORC-VCR
system illustrated in Fig. 1 is described as follows:
With respect to the ORC:
_ exp ¼ m_ ORC ðh1 À h2a Þ ¼ m_ ORC ðh1 À h2s Þgexp
W

ð1Þ

_ exp is the output power from the expander during prowhere W
cess (1-2a) in kW, m_ ORC is the mass flow rate of the working
fluid in the ORC in kg/s, h1 is the expander inlet specific
enthalpy in kJ/kg, h2a is the expander exit actual specific
enthalpy in kJ/kg, h2s is the expander exit isentropic specific
enthalpy in kJ/kg, and gexp is the expander isentropic
efficiency.
_ P ¼ m_ ORC ðh4a À h3 Þ ¼ m_ ORC ðh4s À h3 Þ
W
gP

ð2Þ

_ P is the inlet power to the pump during process (3-4a)
where W
in kW, h4a is the pump exit actual specific enthalpy in kJ/kg, h3
is the pump inlet specific enthalpy in kJ/kg, h4s is the isentropic

Properties of the proposed candidates for ORC-VCR system.

Substance

R1270
R290
RC318
R236fa
R600a
R236ea
R600
R245fa
R1234yf
R1234ze(E)

Chemical formula

CH3ACH‚CH2
C3H8
Cyclo-C4F8
CF3ACH2ACF3
Iso-C4H10
CF3ACHFACHF2
C4H10
CF3ACH2ACHF2
CF3CF‚CH2
CHF‚CHCF3

Physical data

Environmental data
vc  10

3

M

NBP

Tc

g/mol

°C

°C

MPa

m /kg

year

42.08
44.10
200.03
152.04
58.12
152.04
58.12
134.05
114.04
114.04

À47.7
À42.1
À6.0
À1.4
À11. 7
6.2
À0.55
15.1
À29.5
À19.0

92.4
96.7
115.2
124.9
134.7
139.3
152.0
154.1
94.7
109.4

4.67
4.25
2.78
3.20
3.63
3.50
3.80
3.65

3.38
3.64

4.477
4.577
1.613
1.814
4.457
1.776
4.389
1.934
0.0021
0.0020

0.001
0.041
320 0
242
0.016
11.0
0.018
7.7
0.029
0.045

Pc

3

ALT

Safety data

ODP

GWP 100 yr

LFL

0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0

<20
$20
10,300
9820
$20
1410
$20
1050
<1
<1

2.7
2.1
None
None
1.6
None
2.0
None
6.2
7.6

Safety group

%
A3
A3
A1
A1
A3
–
A3
B1
A2L
A2L


Parametric analysis of a combined organic Rankine-vapor refrigeration system
specific enthalpy at the pump outlet in kJ/kg, and gP is the
pump isentropic efficiency.

_ net ¼ W
_ exp À W
_P
W

ð3Þ

_ net is the net output power from the ORC in kW.
where W
Q_ b ¼ m_ ORC ðh1 À h4a Þ

ð4Þ

where Q_ b is the heat transfer rate to the working fluid in the
boiler during the process (4a-1) in kW, h1 is the boiler outlet
specific enthalpy in kJ/kg, and h4a is the boiler inlet actual
specific enthalpy in kJ/kg.
gORC ¼

_ net
W
Q_ b

ð5Þ

where gORC is the organic Rankine cycle efficiency.
With respect to the VCR cycle:
Q_ e ¼ m_ VCR ðh5 À h7 Þ

ð6Þ

where Q_ e is the rate of heat transfer to the working fluid in the
evaporator during process (7-5) in kW, m_ VCR is the mass flow
rate of the working fluid in the VCR in kg/s, h5 is the evaporator outlet specific enthalpy in kJ/kg, and h7 is the evaporator
inlet specific enthalpy in kJ/kg.
_ c ¼ m_ VCR ðh5 À h6a Þ ¼ m_ VCR ðh5 À h6s Þ
W
gc

ð7Þ

_ c is the inlet power to the compressor during process
where W
(5-6a) in kW, h5 is the compressor inlet specific enthalpy
in kJ/kg, h6a is the compressor outlet actual specific enthalpy
in kJ/kg, h6s is the compressor outlet isentropic specific
enthalpy in kJ/kg, and gc is the compressor isentropic
efficiency.
_c ¼W
_ net
W

ð8Þ

The VCR cycle COP is defined as follows:
COPVCR ¼

Q_ e
_c
W

ð9Þ

The COPS can be calculated as follows:
COPS ¼ gORC COPVCR

ð10Þ

The m_ total is defined as follows:
m_ total ¼

m_ ORC þ m_ VCR
Q_ e

Table 2

ð11Þ

655

The compressor compression ratio (CMR) during the process (5-6a) and the expander expansion ratio (EPR) during the
process (1-2a) are measures for the required compressor and
expander sizes, respectively, and described as follows:
p
CMR ¼ 6a
ð12Þ
p5
EPR ¼

v2a

v1

ð13Þ

The performance of the system is characterized by the
COPS and m_ total. The COPS and m_ total are calculated by Eqs.
(10) and (11), respectively. The CMR and EPR are computed
using Eqs. (12) and (13), respectively. The thermodynamic
properties of the proposed candidates are obtained from the
NIST database REFPROP 9.1 [24].
The basic values of the ORC-VCR system operating
parameters and their ranges are presented in Table 2. The
highest boiler temperature was adjusted at 90 °C, which
allowed the usage of waste heat or geothermal energy with a
temperature of approximately 100 °C or a little lower as a heat
source. A computer Excel program was established to assess
the ORC-VCR system performance as well as the CMR and
EPR with various candidates under different working
conditions.
Results and discussion
In this study, the performance of ORC-VCR system using 10
HFCs, HCs and HFOs, i.e. R1270, R290, RC318, R236fa,
R600a, R236ea, R600, R245fa, R1234yf, and R1234ze(E) as
working fluids was calculated and analyzed. Their basic thermodynamic properties, and environmental and safety aspects
are listed in Table 1. The critical temperatures range from
92.42 °C for R1270 to 154.1 °C for R245fa. This range was
specified hoping to find the best working fluid for ORCVCR system to recapture low-grade thermal energy.
A comparison between performances of the basic ORCVCR system using the proposed candidates is listed in Table 3.
Also, the T-s diagram type and the saturated pressure at 90 °C
of the working fluids as well as the actual quality after compressor (x6a) are illustrated in Table 3. The letters o and b

are used for fluids with overhanging and bell-shaped T-s diagram, respectively. In the present study only subcritical systems are studied. The calculations in Table 3 were done
using the basic values of the operating parameters as specified
in Table 2. It can be observed from Table 3 that the general
trend is that with increasing critical temperature, the COPs
increases. The results in Table 3 show that among all

The basic values of the parameters utilized in the ORC-VCR system and their ranges.

Parameter

Basic value

Range

Mass flow rate of the working fluid in ORC
Isentropic efficiency of the feed pump
Boiler temperature
Isentropic efficiency of the expander
Condenser temperature
Evaporator temperature
Isentropic efficiency of the compressor

1.0 kg/s
75%
80 °C
80%
40 °C
5 °C
75%

–
–
60–90 °C
60–90%
30–55 °C
À15 °C to 15 °C
60–90%


656
Table 3

B. Saleh
Performance of the basic ORC-VCR system utilizing the proposed working fluids.

Substance

Cycle type

Psat, MPa

gORC, %

COPVCR

COPS

m_ total  100

EPR

CMR

x6a

R1270
R290
RC318
R236fa
R600a
R236ea
R600
R245fa
R1234yf
R1234ze(E)

b
b
o
o
o
o
o
o
o
o

4.467
3.764
1.668

1.565
1.641
1.263
1.250
1.004
3.080
2.4755

6.71
6.90
6.94
7.37
7.57
7.55
7.76
7.77
6.78
7.28

4.80
4.81
4.58
4.88
5.01
4.96
5.12
5.12
4.68
4.89

0.322
0.332
0.318
0.360
0.380
0.375
0.398
0.398
0.317
0.356

1.41
1.32
3.98
2.63
1.11
2.36
0.97
1.84
3.12
2.40

2.65
2.70
3.24
3.23
2.75
3.21
2.81
3.26

3.13
3.02

2.44
2.48
3.15
3.33
2.85
3.50
3.04
3.76
2.73
2.96

–
–
0.93
0.99
–
0.99
–
–
–
–

candidates, R600 and R245fa with the highest critical temperatures have the maximum and the same COPS values, whereas
RC318, R1234yf, and R1270 with the lowest critical temperatures have the minimum COPS values. On the other hand,
R600 accomplishes the lowest m_ total, while RC318 attains the
highest m_ total. So from the viewpoint of thermodynamics,
R600 can be considered a superior candidate for ORC-VCR

system for recovering low-grade thermal energy.
The effects of different operating conditions such as the
evaporator, condenser, and boiler temperatures, in addition
to the compressor and expander isentropic efficiencies on the
ORC-VCR system performance, are discussed in the following
sections. In each case, only varies the parameter whose effect is
studied within the given range in Table 2 while the remaining
parameters are fixed and equal to the basic values given in
Table 2. The analyses are exhibited graphically in Figs. 3–6.
The influence of boiler temperature on the system performance
Fig. 3 exhibits the influence of boiler temperature on the basic
ORC-VCR system performance. Fig. 3a displays the alteration
in COPS as a function of the boiler temperature for different
candidates in the basic ORC-VCR system. This figure shows
that the COPS of the system improves as the boiler temperature increases for all candidates. Among the proposed working
fluids, R600 and R245fa achieve the highest COPS for all boiler temperatures, while RC318, R1234yf, and R1270 attain the
lowest COPS. The COPS values of R245fa are approximately
the same as those of R600. They have the highest critical temperatures (Tc, R245fa = 154.05 °C, Tc, R600 = 151.98 °C).
When the boiler temperature increases from 60 to 90 °C, the
COPS using R245fa or R600 improves by about 107.0%.
When the boiler temperature is 90 °C, the COPS using both
working fluids is 0.47, which is greater than those of RC318,
R1234yf, and R1270 by approximately 28.0%, 33.8%, and
35.3%, respectively. The maximum system pressures using
R600 and R245fa are the lowest among all candidates, reaching 1.250 and 1.004 MPa, respectively, at a boiler temperature
of 90 °C as exhibited in Table 3, resulting in lower system
investment.
R245fa has a high GWP of 1050 and is characterized in
safety group B1; contrariwise, R600 has a very low GWP of
20 and is characterized in safety group A3 as shown in Table 1.

Consequently, R600 can be considered as a promising candidate for the ORC-VCR system to recover low-grade thermal
energy with a temperature range from 60 °C to 90 °C.

Fig. 3 The effect of boiler temperature on the COPS (a), m_ total
(b) and EPR (c) for various candidates in the basic ORC-VCR
system.


Parametric analysis of a combined organic Rankine-vapor refrigeration system
Fig. 3b shows the influence of boiler temperature on the
m_ total for different candidates in the basic ORC-VCR system.
This figure exhibits that the m_ total reduces as the boiler temperature increases for all proposed working fluids. Within the
studied boiler temperature range, R600 attains the lowest
m_ total, while RC318 achieves the highest m_ total which has the
highest molecular mass (200.03 kg/kmol).
Fig. 3c exhibits the change in EPR values as a function of
the boiler temperature for different candidates in the basic
ORC-VCR system. This figure shows that the EPR rises as
the boiler temperature increases for all candidates. This is
due to the rise of saturation pressure with the temperature.
The EPR values at a boiler temperature of 90 °C are nearly
twice those at 60 °C for all candidates. The maximum EPR
is achieved by R245fa, but when the boiler temperature was
between 80 and 90 °C the maximum is attained by RC318.
The minimum EPR is attained by R1270, but when the boiler
temperature ranges from 84 to 90 °C the lowest is accomplished by R600a. As shown in the figure the candidates can
be divided into three groups, the first one contains HFCs candidates, i.e. RC318, R236fa, R236ea, and R245fa where they
have the highest and nearly the same values of EPR. The sec-

657

ond group contains HCs candidates, i.e. R1270, R290, R600a,
and R600 where they have the lowest EPR values and the variations in the EPR values are slight. The maximum difference is
about 7.0% between R1270 and R600. The third group contains HFOs candidates, i.e. R1234yf and R1234ze(E) where
their EPR values are in between those of HFCs and HCs
groups. Moreover, the EPR should be lower than 50 to accomplish a turbine efficiency higher than 80% [25]. As exhibited in
Fig. 3c, the EPR for all candidates is less than 4.5; consequently, expander efficiency greater than 80% can be
accomplished.
The influence of condenser temperature on the system
performance
The variation of COPS with the condenser temperature for all
candidates in the basic ORC-VCR system is illustrated in
Fig. 4a. It is observed from the figure that, the condenser temperature has a large effect on the COPS. This is because the
condenser temperature has an effect on both VCR cycle and
ORC individually. The rejected heat is governed by condenser

Fig. 4 The effect of condenser temperature on the COPS (a), m_ total (b), EPR (c) and CMR (d) for various candidates in the basic
ORC-VCR system.


658
temperature, which is an additional parameter to boost the
cycle efficiency in addition to the boiler temperature. Small
values of rejected heat are preferable to achieve high efficiencies in both cycles. It can be noticed from Fig. 4a that the
COPS reduces with the increase in condenser temperature for
all candidates. This is justified by the truth that as the temperature and pressure kept constant at the inlet of the compressor,
the increase in condenser temperature causes the rise of
pressure and enthalpy at the compressor exit. This leads to
the decrease in COPS and the increase in CMR according to
Eqs. (6–9) and (13). When the condenser temperature rises

B. Saleh
from 30 to 55 °C, the COPS reduces by about 21% for all candidates. Among the proposed working fluids, R600 and
R245fa achieve the highest and approximately the same COPs
values for all condenser temperatures, while RC318 attains the
lowest COPS.
The variation of m_ total with the condenser temperature for
various candidates in the basic ORC-VCR system is displayed
in Fig. 4b. Generally, the increase in condenser temperature
leads to increase of m_ total for all candidates. R600 attained
the lowest m_ total, while the highest was achieved by RC318
for all condenser temperatures. Compared with other candidates, R600 can be considered the best one. At condenser temperature of 30 °C and the basic values for the remaining
parameters, the COPS and m_ total using R600 are 0.718 and
0.006 kg/(s kW), respectively.
The influences of condenser temperature on the EPR and
the CMR for different working fluids in ORC-VCR system
are illustrated in Fig. 4c and d, respectively. It is detected from
these figures that with the increase in condenser temperature,
the EPR decreases while the CMR increases. This is logically
when taking into account the thermophysical properties effect
of these candidates. The variations between the EPR values for
the proposed working fluids are smaller at high than that at
low condenser temperatures. The reverse is valid for the
change of the CMR with the condenser temperature. The
working fluids in Fig. 4c can be divided into three groups:
the first one includes the HFCs candidates (R245fa, R236ea,
R236fa, and RC318) which include the largest values of
EPR. The EPR values of this group are approximately the
same. The second group contains the HCs candidates (R600,
R600a, R290, and R1270) which include the smallest values

of EPR. The differences between the EPR values for this group
are teeny at condenser temperature greater than 50 °C. The
third group contains HFOs candidates (R1234ze(E) and
R1234yf) in which the EPR values are in between those of
HFCs and HCs groups.
The influence of evaporator temperature on the system
performance

Fig. 5 The effect of evaporator temperature on the COPS (a),
CMR (b) and m_ total (c) for various candidates in the basic ORCVCR system.

Fig. 5 displays the influence of evaporator temperature on the
COPS, CMR and m_ total, respectively for different candidates in
the basic ORC-VCR system. It can be noticed from Fig. 5a
that, the increment in evaporator temperature leads to
improvement of the COPS. This can be interpreted by the truth
that with the increase in evaporator temperature its saturation
pressure increases, which results in decreasing the CMR, as
displayed in Fig. 5b. This causes the required work for the
compressor to decrease at the particular working conditions.
Also as the evaporator temperature rises, the cooling capacity
improves due to the increment in refrigeration effect. Both
effects boost the ORC-VCR system COPS. In addition to the
improvement of COPS with the rise of evaporator temperature
for all candidates, the reduction in m_ total is nearly linear as
observed from Fig. 5c. Among the proposed candidates,
R600 and R245fa attain the highest and approximately the
same COPS values, while R600 has the lowest m_ total values
for all evaporator temperatures. With the increase in evaporator temperature from À15 to 15 °C using R600, the COPS
improves by approximately 180.0%, while m_ total declines by

about 52.0%.


Parametric analysis of a combined organic Rankine-vapor refrigeration system

659

Fig. 6 The effect of expander and compressor isentropic efficiencies on the COPS (a), (b) and m_ total (c), (d) for various candidates in the
basic ORC-VCR system.

The influence of compressor and expander efficiencies on the
system performance
Fig. 6 shows the variations of COPS and m_ total as a function
of the compressor and expander isentropic efficiencies for
different candidates in the basic ORC-VCR system. It can
be observed from Fig. 6a and b that the expander and
compressor efficiencies have a considerable effect on the
COPS. As the compressor and expander isentropic efficiencies increase, the COPS improves nearly linearly for all candidates. As the expander efficiency varies from 60% to 90%,
the COPS increments by about 53% for all working fluids.
While as the compressor efficiency increases from 60% to
90%, the COPS improves by about 50% for all candidates.
It can be seen from Fig. 6c and d that, the expander and
compressor efficiencies have a weak effect on m_ total except
in the case of RC318. With the enhancement of the compressor and expander isentropic efficiencies, the decrement
in m_ total is almost linear.
To sum up the above discussion, there is still no substance
that totally meets the whole requirements from the viewpoint
of COPS, m_ total, EPR, CMR, and environmental and safety
aspects. Since the present study focuses on the performance
of the ORC-VCR system from the viewpoint of thermodynamics, the system performance is characterized by COPS and

m_ total. Compared with all candidates, R600 achieves the highest COPS and the lowest m_ total under all considered operating

conditions. Furthermore, it should be mention that the emphasis of this study is to assess the performance of HFCs, HCs,
and HFOs in the ORC-VCR system; therefore, the studied system is simple. To improve the system performance, internal
heat exchangers should be added. This shows that the ORCVCR system is a superior system for conversion of low-grade
thermal energy to cooling or electricity.
Up to now, the thermodynamic aspects of the proposed
candidates for ORC-VCR system are considered. On the other
side, the safety and environmental issues of the proposed candidates for the ORC-VCR system should be taken into
account during selection of the working fluids. Among the proposed candidates, the HFCs group, i.e. R236fa, R236ea,
R245fa, and RC318 are non-flammable but they have the maximum GWP. Therefore, they need special attention concerning
environmental aspects. On the other hand, the HCs candidate
group, i.e. R1270, R290, R600a, and R600 have the advantage
of being very low GWP; however, they are flammable. Accordingly, the safety issues should receive extra attention. The new
HFOs candidates group, i.e. R1234yf and R1234ze(E) have a
GWP less than 1 and are mildly flammable working fluids with
ASHRAE safety classification of 2L. Therefore, from the viewpoint of environmental and safety aspects, there is no an ideal
working fluid for the ORC-VCR system, and every candidate
has advantages and disadvantages. Consequently, there is no
working fluid exist now that totally meet the energy efficiency,
safety and environmentally friendly. The only actual


660
controversy against using of R600 is the flammability. However, with satisfactory safety precautions, the flammability will
not constitute a problem in using R600.

B. Saleh

[5]

Conclusions
[6]

In the present research, the performance of ORC-VCR system
activated by low-grade thermal energy is investigated. Some
common hydrofluorocarbons and hydrocarbons, as well as
new hydrofluoroolefins, i.e. R1270, R290, RC318, R236fa,
R600a, R236ea, R600, R245fa, R1234ze(E), and R1234yf,
are proposed as working fluids. The effects of evaporator, condenser, and boiler temperatures, in addition to the compressor
and expander isentropic efficiencies on the ORC-VCR system
performance are also examined and discussed.
The results indicate that all studied parameters have comparable influences on the ORC-VCR system performance for
all candidates. In detail, as the evaporator and boiler temperatures as well as the compressor and expander isentropic efficiencies increase, the COPS improves while the m_ total
decreases for all candidates. The reverse is valid for the condenser temperature. Also, as the evaporator and boiler temperatures increase, the compression ratio reduces and the
expansion ratio increases, respectively, while the reverse occurs
with the condenser temperature.
From the acquired results it can be concluded that, among
all candidates, R600 and R245fa achieve the highest and
approximately the same COPS values, while R600 achieves
the lowest m_ total under all considered operating conditions.
Due to environmental issues of R245fa, R600 is recommended
as a superior candidate for the ORC-VCR system for retrieving low-grade thermal energy in a temperature range from
60 °C to 90 °C from perspectives of environmental concerns
and system performance. With condenser temperature of 30 °
C and the basic values for the remaining parameters, the maximum COPS and the corresponding m_ total using R600 are 0.718
and 0.006 kg/(s kW), respectively.
Conflict of Interest

[7]

[8]
[9]

[10]

[11]

[12]

[13]
[14]

[15]

[16]

[17]

[18]

The authors have declared no conflict of interest.
[19]

Compliance with Ethics Requirements

[20]

This article does not contain any studies with human or animal
subjects.

[21]

References

[22]

[1] Wang H, Peterson R, Harada K, Miller E, Ingram-Goble R,
Fisher L. Performance of a combined organic Rankine cycle and
vapor compression cycle for heat activated cooling. Energy
2011;36:447–58.
[2] Srikhirin P, Aphornratana S, Chungpaibulpatana S. A review of
absorption refrigeration technologies. Renew Sust Energy Rev
2001;5:343–72.
[3] Chunnanond K, Aphornratana S. Ejectors: applications in
refrigeration
technology.
Renew
Sust
Energy
Rev
2004;8:129–55.
[4] Kim KH, Perez-Blanco H. Performance analysis of a combined
organic Rankine cycle and vapor compression cycle for power

[23]

[24]

[25]

and
refrigeration
cogeneration.
Appl
Therm
Eng
2015;91:964–74.
Aneke M, Agnew B, Underwood C, Menkiti M.
Thermodynamic analysis of alternative refrigeration cycles
driven from waste heat in a food processing application. Int J
Refrig 2012;35:1349–58.
Saleh B, Koglbauer G, Wendland M, Fischer J. Working fluids
for low temperature organic Rankine cycles. Energy
2007;32:1210–21.
Prigmore D, Barber R. Cooling with the sun’s heat design
considerations and test data for a Rankine cycle prototype. Sol
Energy 1975;17:185–92.
Nazer MO, Zubair SM. Analysis of Rankine cycle airconditioning systems. ASHRAE J 1982;88:332–4.
Eg˘rican AN, Karakas A. Second law analysis of a solar powered
Rankine cycle/vapor compression cycle. J Heat Recov Syst
1986;6:135–41.
Kaushik SC, Singh M, Dubey A. Thermodynamic modelling of
single/dual organic fluid Rankine cycle cooling systems: a
comparative study. Int J Ambient Energy 1994;15:37–50.
Kaushik SC, Dubey A, Singh M. Thermal modelling and energy
conservation studies on Freon Rankine cycle cooling system
with regenerative heat exchanger. Heat Recov Syst CHP
1994;14:67–77.
Wang H, Peterson R, Herron T. Design study of configurations

on system COP for a combined ORC (organic Rankine cycle)
and VCR (vapor compression cycle). Energy 2011;36:4809–20.
Jeong J, Kang YT. Analysis of a refrigeration cycle driven by
refrigerant steam turbine. Int J Refrig 2004;27:33–41.
Aphornratana S, Sriveerakul T. Analysis of a combined
Rankine-vapour compression refrigeration cycle. Energy
Convers Manage 2010;51:2557–64.
Bu X, Wang L, Li H. Performance analysis and working fluid
selection for geothermal energy-powered organic Rankine-vapor
compression air conditioning. Geotherm Energy 2013;1–2:1–14.
Yue C, You F, Huang Y. Thermal and economic analysis of an
energy system of an ORC coupled with vehicle air conditioning.
Int J Refrig 2016;64:152–67.
Mole´s F, Navarro-Esbrı´ J, Peris B, Mota-Babiloni A,
Kontomaris K. Thermodynamic analysis of a combined
organic Rankine cycle and vapor compression cycle system
activated with low temperature heat sources using low GWP
fluids. Appl Therm Eng 2015;87:444–53.
Jung D. Editorial: energy and environmental crisis: let’s solve it
naturally in refrigeration and air conditioning. HVAC&R Res
2008;14:631–4.
Venkatarathnam G, Murthy SS. Refrigerants for vapour
compression refrigeration systems. Resonance 2012;17:139–62.
Palm B. Hydrocarbons as refrigerants in small heat pump and
refrigeration systems – a review. Int J Refrig 2008;31:552–63.
Sethi A, Becerra EV, Motta SY. Low GWP R134a replacements
for small refrigeration (plug-in) applications. Int J Refrig
2016;66:64–72.
Calm JM, Hourahan GC. Physical, safety, and environmental
data summary for current and alternative refrigerants. ID: 915.

In: Proceedings of the 23rd international congress of
refrigeration, 2011 August 21–26, Prague, Czech Republic. p.
1–22.
IPCC. Intergovernmental Panel on Climate Change (IPCC),
Fifth Assessment Report: Climate Change, Geneva,
Switzerland; 2013.
Lemmon EW, Huber ML. Reference fluid thermodynamic and
transport properties-REFPROP version 9.1.. Boulder,
Colorado, USA: National Institute of Standards and
Technology (NIST); 2013.
Invernizzi C, Iora P, Silva P. Bottoming micro-Rankine cycles
for micro-gas turbines. Appl Therm Eng 2007;27:100–10.